论文标题
星际冰类似物的紫外线光处理后，NH2CHO和CH3CHO的形成
Formation of NH2CHO and CH3CHO upon UV photoprocessing of interstellar ice analogs
论文作者
论文摘要
复杂的有机分子（COM）可以通过在灰尘晶粒顶部积聚的星际冰披风的能量加工来产生。两个具有拟议的冰形成途径的COM是甲酰胺和乙醛。两者都在太阳系彗星以及不同的星际和星际环境中检测到。在这项工作中，我们研究了CO：NH3和CO：CO：CH4 ICE样品的紫外光处理后的NH2CHO和CH3CHO形成。在探索的实验条件下，从NH2自由基到NH2CHO的转化是从CH3自由基到CH3CHO的转化率的2-16倍，这可能是因为后者的形成与较大的碳氢化合物的形成竞争。另外，随着冰中的NH3丰度的增加，NH2在10 K时的转化为NH2CHO，并且随着共同主导的CO：NH3 ICES的温度而增加。这与形成NH2CHO形成的小NH2和HCO重新定向屏障的存在是一致的，NH2CHO的形成随着冰温的升高而被克服。测得的NH2CHO和CH3CHO形成效率和速率与在可比条件下相同冰样品的电子照射期间发现的效率相似，这表明紫外光子和宇宙射线都对这些物种在太空中的固态形成的贡献都相似。最后，测得的转化率产量（NH2CHO的最高数量级）表明，在观察到的NH2CHO/CH3CHO丰度比为0.1的情况下，可能还有额外的冰和/或气相构造途径。
Complex organic molecules (COMs) can be produced by energetic processing of interstellar ice mantles accreted on top of dust grains. Two COMs with proposed energetic ice formation pathways are formamide and acetaldehyde. Both have been detected in Solar System comets, and in different circumstellar and interstellar environments. In this work, we study the NH2CHO and CH3CHO formation upon UV photoprocessing of CO:NH3 and CO:CH4 ice samples. The conversion from NH2 radicals to NH2CHO is 2-16 times higher than the conversion from CH3 radicals to CH3CHO under the explored experimental conditions, likely because the formation of the latter competes with the formation of larger hydrocarbons. In addition, the conversion of NH2 into NH2CHO at 10 K increases with the NH3 abundance in the ice, and also with the temperature in CO-dominated CO:NH3 ices. This is consistent with the presence of a small NH2 and HCO reorientation barrier for the formation of NH2CHO, which is overcome with an increase in the ice temperature. The measured NH2CHO and CH3CHO formation efficiencies and rates are similar to those found during electron irradiation of the same ice samples under comparable conditions, suggesting that both UV photons and cosmic rays would have similar contributions to the solid-state formation of these species in space. Finally, the measured conversion yields (up to one order of magnitude higher for NH2CHO) suggest that in circumstellar environments, where the observed NH2CHO/CH3CHO abundance ratio is 0.1, there are likely additional ice and/or gas phase formation pathways for CH3CHO.
